The invention relates to an infinitely variable traction roller transmission in which motion is transmitted from an input toric disc to an output toric disc through traction rollers pivotally supported between the toric discs, the discs being forced toward each other for engagement with the traction rollers therebetween.
Generally, the engagement forces are obtained by an axial cam structure which provides for an axial force dependent on the torque transmitted through the transmission. Such an arrangement is shown, for example, in U.S. Pat. No. 4,086,820, which is assigned to the assignee of the present application.
It has been found however that, in a high speed reduction mode, the cam structure produces contact forces far in excess of what is needed for slip-free power transmission since the traction rollers are then in engagement with the radially inner area of the input toric disc which, in this position, is wedged between the rollers by the axial forces. The angle of contact at this point--with respect to the axis of the toric disc--is an acute angle .alpha. so that the contact force Fc is substantially larger than the part of the axial cam force Fa.sub.1 generating the particular contact force, that is, EQU Fc=Fa.sub.1 /sin .alpha..
If .alpha. is, for example, 30.degree. then EQU Fc=Fa.sub.1 /1/2=2Fa.sub.1 ;
that is, the contact force is twice the corresponding cam force. Accordingly, greater contact forces than needed are generated, resulting in greater than necessary wear and friction, and furthermore in outward deflection of the traction roller support structures and also in excessive cam lift and possible jumping of the cam rollers over the cam crests.